As a container to store contents of mainly a liquefied element (for example, cosmetics), such as a liquid or a gel, there is a container referred to as an “overmolded container”. This overmolded container has a configuration in which a hollow body to be filled with the contents (hereinbelow, referred to as “inner bottle”) is integrally covered with an outer body made by injection molding (hereinbelow, referred to as “outer”) of molten resin. As a method of forming this overmolded container, for example, as described in Japanese Patent Application Laid-open Publication No. 06-23758, the inner bottle is manufactured by blow molding or the like, and then the molten resin is injected to an outer side of the inner bottle to form the outer, and thereby the inner bottle and the outer are integrated.
With this overmolded container, for example, by covering the inner bottle made of colored resin with an outer formed of light permeable resin that is transparent or in a ground glass state or a colored glass state, light can be shielded from the contents in the inner bottle to prevent quality deterioration due to outside light, while providing a feel similar to glass and an aesthetically pleasing texture that gives a sense of profoundness and high quality. Further, this container is provided with impact resistance and degrees of freedom in shape since it is made of the resin. Further, in the case of forming decoration of letters and drawings on the outer surface of the inner bottle, and forming the outer with a light permeable resin so that the decoration can be seen through it, an effect can be achieved that the decorated portion is not exposed on the outer surface of the overmolded container, and the product name and the like will not peel off or wear off in principle.
With the overmolded container, however, when injecting the molten resin to an outer surface of the inner bottle and integrating the outer thereon, there is a possibility that the inner bottle deforms or is damaged by the pressure and heat of the molten resin. For example, with the invention described in Japanese Patent Application Laid-open Publication No. 06-23758, the overmolded container is formed by a method in which a core material made of a mixture of superabsorbent resin and water is filled in a preformed shell like an inner bottle and the mixture is frozen and then the shell with the frozen mixture therein is set in a mold for injecting a molten resin for the outer. After forming the outer, the core material inside the inner bottle is melted and removed. But, with this method, the operation in each step becomes complicated, and the number of steps increases, thus resulting in increase in forming cost. Further, in the case the core material cannot be completely removed, the contents to be actually stored inside the inner bottle will be contaminated by the remains of that core material.
With the technique disclosed in Japanese Patent Publication No. 4377447, however, there will be no serious problem if the inner bottle is spherical. However, when molding a cylindrical inner bottle with a cover of outer by injecting the molten resin, there will be serious problems. Because, when forming the outer, a flowing molten resin will remain in a corner portions such as boundaries between a side surface and end surfaces of the cylinder, and a great pressure and heat are applied on the corner portions, and thereby the corner portions will be crushed and deformed. Further, in the case there is decoration on the outer surface of the inner bottle, there is a possibility that the decorated portion flows due to heat from the molten resin, and the appearance of the decorated portion may be deteriorated or may not function as a decoration at all.
Therefore, a solution of cooling the hollow inner portion of the inner bottle may be considered, but if there is an error in a cooling portion or a cooling timing, the resin that becomes the outer may set without spreading in the entire mold and namely a short shot may occur. Note that with the technique described in Japanese Patent Publication No. 4377447, since the inner bottle is closed while molding the outer, it is extremely difficult to perform cooling itself.